Fittings known from prior art exhibit supporting bodies which, on the outer peripheral surface, exhibit a continuous groove, in which a gasket element, for example a sealing O-ring, can be arranged. In order to join a pipe with the fitting, a pipe end is placed on the supporting body, so that the supporting body engages into the pipe. The outer diameter of the supporting body and the inner diameter of the pipe are here preferably adapted to each other. The tightness of the connection is caused by the preferably resilient gasket element projecting out of the groove, which is compressed between the inner peripheral surface of the pipe and the groove of the supporting body, so that it tightly abuts the two surfaces.
However, the flow cross section of the pipe is narrowed at the joining site between the pipe and the fitting by the engagement of the supporting body into the pipe. For example, this can impair the flow behavior of a fluid by generating turbulences and/or a pressure drop of the pressurized fluid at the joining site. In addition, the provision of a gasket element as an extra, in particular movable element increases the caution a user must exercise in manufacturing the permanent joint.
In order to avoid the aforementioned disadvantages, use could be made of a fitting that exhibits an outer body. The inner diameter of the outer body and outer diameter of the pipe are in this case adapted to each other, so that the outer body of the fitting embraces a pipe end. In such a fitting, the seal could be established between the inner peripheral surface of the outer body and outer peripheral surface of the pipe by arranging an O-ring in a continuous groove situated on the inner peripheral surface of the outer body. This made it possible to minimize a narrowing of the flow cross section of the pipe by making the supporting body smaller, or even to completely avoid said narrowing by omitting the supporting body.
However, this type of seal is not suitable for composite pipes, which exhibit several layers of different materials bonded together, sometimes with adhesive. A fluid carried in the pipe or, respectively, the fitting can come into contact with or, respectively, wet the facing edge of the pipe end at which the joining sites of the materials of the composite pipe are exposed, thereby potentially impairing the cohesion of individual layers of the composite pipe, for example through moistening, and hence tightness as well.